"Supersaturated" self-assembled charge-selective interfacial layers for organic solar cells

Area of Science:

• Organic electronics
• Materials science
• Photovoltaics

Background:

• Organic photovoltaic (OPV) cells require efficient interfacial layers (IFLs) for optimal charge extraction.
• Tin-doped indium oxide (ITO) is a common anode material in OPVs, but its surface properties can limit device performance.
• Achieving densely packed, charge-selective IFLs is crucial for enhancing OPV efficiency.

Purpose of the Study:

• To synthesize and characterize novel organosilane-based interfacial layers (IFLs) for ITO anodes in OPVs.
• To investigate the impact of "supersaturated" heterogeneous self-assembled monolayers (SHSAMs) on IFL packing density and properties.
• To evaluate the performance enhancement of OPV devices utilizing these novel SHSAM IFLs.

Main Methods:

• Synthesis and characterization of Ar2N-(CH2)n-SiCl3 organosilane precursors.
• Deposition of heterogeneous self-assembled monolayers (SAMs) by co-deposition of precursors with varying chain lengths (n=3, 6, 10, 18).
• Characterization using contact angle, X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), cyclic voltammetry, and DFT computation.
• Fabrication and testing of bulk-heterojunction OPV devices (PTB7:PC71BM) with SHSAM IFLs.

Main Results:

• SHSAMs achieved up to 17% higher headgroup densities compared to homogeneous SAMs.
• IFL properties were significantly modified, with work function increased by up to 16% and areal dipole moment by up to 49%.
• OPV devices with SHSAM IFLs showed a 54% increase in power conversion efficiency (PCE) and a 35% increase in open-circuit voltage (Voc).

Conclusions:

• The developed SHSAMs effectively enhance interfacial charge selectivity and collection in OPVs.
• The improved performance is attributed to favorable band bending and altered Schottky barrier height induced by the SHSAMs.
• SHSAM IFLs offer a promising alternative to conventional PEDOT:PSS, achieving competitive or superior OPV performance.